Jim Michalak's Boat Designs

(15jan06) This issue continues ballast calculations. The 1feb06 issue
will begin the discussion of a new design.

THE BOOK IS OUT!

BOATBUILDING FOR BEGINNERS (AND BEYOND)

is out now, written by me and edited by Garth Battista of Breakaway Books. You might find it at
your bookstore. If not check it out at the....

ON LINE CATALOG OF MY
PLANS...

...which can now be found at Duckworks
Magazine. You order with a shopping cart set up and pay with credit
cards or by Paypal. Then Duckworks sends me an email about the order
and then I send the plans right from me to you.

Left:

Tim Merrill made this great QT rowing skiff, his first boat, from
the plans in my book.

Contents:

Contact info:

IMB Capsize Test

WE CAPSIZE IMB....

The IMB design has been around a while. It was designed for a contest
put on ten years ago by International Marine Publishing. So I called it
the "International Marine Beacher" which became IMB. I'm featuring the
IMB below in the design section if you want to read more details but in
general it was supposed to be a self righting mini (13' x 5') cruiser
that could be pulled behind a small car.

To keep the weight way down I made it a Birdwatcher boat with a cabin
style invented by Phil Bolger in the mid '80's. Everyone rides inside a
watertight cabin looking out through Plexiglass windows. Their weight
is kept low and thus becomes the boat's ballast. That plus the high
cabin sides might make the boat self righting to 90 degrees of roll, I
hoped.

But we were finding it was not all that foolproof. Scram Pram, which is
a 16' x 6' version of IMB, was tested to capsize twice (once
accidentally, once on purpose) and found to lie stable on its side when
knocked down to 90 degrees. That was not much of a worry since Scram is
supposed to have 300 pounds of water ballast and when that ballast was
tried on the prototype, the boat quickly self rigthed from 90 degrees.
There was a feeling that much less ballast was needed. But the fact was
that with one large crewmember inside acting as ballast, the Scram
would not self right without the water ballast.

So I was concerned about the smaller IMB.

I was very fortunate to be able to attend the Lake Conroe (Houston)
messabout. Among all the attractions were two IMB's! They are the only
ones I know of. The first was built by Gerry Scott and the second by
Bob Williams.

I got to sail in both, although the "sailing conditions" were light to
say the least.

At this messabout there is a tradition of turning over someone's boat!
That is where the Scram tests were done a couple of years back. Could
we please turn over an IMB?

Gerry Scott was a great sport about it.

Here is what we did. The IMB was beached and we removed the trolling
motor and battery and all the loose things. The boat was walked into
waist deep water, parallel to the shore, and human anchors placed at
bow and stern. The halyard was secured to the mast and its free end
given to me close to the shore. So I could pull the boat over with the
halyard while the good folks held the boat in place.

The sail was stowed to keep tangles to a minimum but the sail and boom
can have an effect on the result. I would expect the boat would be
slightly less stable due to the weight of the sail and boom up high.
Once the boat is knocked down the boom and sail can help float the boat
and keep the boat from going turtle. In fact that effect is really
strong with a lug sail who's yard acts like a float out on the top of
the mast. Then when it comes time to right the boat it is very very
important to totally release the sheet because if water pools in the
sail as you try to raise it off the water the weight of that water can
make the boat much harder to right.

Remember that the skipper's weight is ballast in a boat like this.
Gerry was skeptical about riding inside through the test so he watched
from the outside.

I pulled it over slowly. I can't recall a point where the righting
moment peaked but I would expect it to be at maybe 30 degrees or so.
When the windows start to into the water the empty IMB still has a lot
of righting ability (Gerry says he has sailed his with the windows
touching the water). Somewhere about 80 degrees of heel the righting
moment, as felt by tension in the halyard used to pull the boat over,
went to zero and she wanted to go the rest of the way onto her side. I
eased it down and let the mast into the water at which point the roll
stopped and she was stable on her side.

Now time to right the boat. I held the halyard slack as Tim Weber
attempted to push down on the skeg and see how much effort was needed
to right the boat. Up she popped quickly. Tim said it was pressure of
one hand that did it, maybe 15 pounds. Once it got past the 80 degree
point it righted by itself and I did my best to ease it upward since
these things can roll upright very quickly indeed.

Next Gerry, great sport that he is, said we should repeat the test with
himself inside to check on the human ballast effect (adding that a seat
belt would be nice). So he got inside and braced himself hanging on to
the mast.

Repeating the test was quick and simple although the effort to haul it
over was quite a bit greater with Gerry's ballast inside. We pulled her
over slowly to make sure Gerry had time to brace himself as required.
You might image what being inside would be like, and I'm thinking of
that old Fred Astaire film where he dances in a rotating room the final
affect being that he goes from dancing on the floor then on to the
walls and then for a stint at dancing upside down on the ceiling.
Anyway, here is the scene close to 90 degrees with Gerry smiling and
waving to the crowd, something he might not do in a real capsize.

Unlike the Scram, the smaller IMB had positive righting all the way to
90 degrees. There was tension on the halyard the entire range. When it
came time right the boat no external push was needed, Gerry's weight
and the boat's geometry did it all.

Well, that made me feel better. I'm not sure why the IMB would self
right from 90 degrees when the larger Scram wouldn't except to say that
on the smaller boat the crew's weight might be a larger percentage of
the total making it in effect "more ballasted". On the other hand, the
Scram has higher sides - so go figure. But one thing is for sure. You
can't really take self righting for granted. You really should test.
Changes in construction can upset the equation too.

Unlike the AF3, the Birdwatcher cabin on IMB not only brings the boat
back upright without anyone going for a swim, the boat when upright is
ready to go again. Nothing has flooded and she is dry inside.

But as with any boat it is worth repeating that the knockdown, even a
controlled one, is somewhat violent and anything that isn't secure will
go flying around. So if you sail in knockdown conditions everything
needs to be strapped down. More easily said than done and don't look to
me as an example.

IMB

IMB features a "Birdwatcher" cabin, full length with panoramic
windows and a center walkway slot in the roof. Everyone rides inside.
This style of boat was invented by Phil Bolger in the early 1980's.

These boats can be self righting with minimal, or no, ballast because
crew weight works as ballast. They sit low looking out through the
windows (although standing in normal winds is quite acceptable). The
cabin sides provide lots of buoyancy up high to ensure a good range
of stability. IMB, which is small with a light bottom, should
reliably self right from 60 or 70 degrees and in the test described
above self righted from a full 90 degrees of roll.

These boats are operated from within the cabin, like an automobile.
No one need ever go on deck. For boating with children I can see no
equal.

These are usually cool inside. The tinted windows cut the sun's
power. The crew can sit in the shade of the deck. Downdraft from the
sail cascades through the walkway. (By the way, at the Conroe
messabout two boaters with Lexan windows noted that mosquito spray
will ruin Lexan with one application and they noted belatedly that
the back of the spray can says so.)

IMB has an 8' long cabin on a multichine pram hull. The prototype was
built to perfection by Gerry Scott of Cleveland, Texas. At the Conroe
(Houston) messabout I got a chance to look over his boat plus the
only other IMB I know of built by Bob Williams. Both boats were quite
true to the plans. Both had added low inside seats which made them
more pleasant to use to the point that I will show some seats on the
plans. I was worried when I drew IMB that the headroom would be
minimal so drew no seats thinking the crew would sit on the floor, as
with the original Birdwatcher.

While I was sailing with Gerry, Bob's boat came out on the lake with
four adult males and no sign of bogging down, showing that these fat
pram shapes, very much like my Piccup Pram, can handle a lot of
weight in the 13.5' length.

(Later they rescued a mermaid and returned to the dock with five
total.)

I don't know if either boat had ever been weighed and the 350 pounds
I quote as the empty weight is just a guess. One of the ideas behind
the boat was that it might be towed behind a compact car and I was
glad to see that Gerry tows his behind a 1500cc mini SUV.

Both men adjusted well to the lug sail/leeboard rig. Gerry's has the
blueprint 104 square foot sail and Bob's uses the 114 square foot
Bolger Windsprint sail available from Payson. I used to worry a bit
about running a leeboard on a full cabin boat like this since
handling must be done by remote control, so to speak. No problem.
Both boats have the leeboard lanyard running to a cleat on the aft
deck. The leeboard position is plainly in view at all times through
the cabin window. In use these leeboards need only lanyards to pull
them down. Once down they will usually stay down until they strike
something. Then they pop up and you will need to pull them down
again. I've never seen a need for a lanyard to pull the board up
although I've seen several rigged that way. The Dovekie design had
elaborate cam operated levers in the cabin that operated the
leeboards and I thought that all very clever. But in talking to some
Dovekie owners I found the internal levers are not universally loved
since they can often be in the way. Anyway, my idea was not to run
the down lanyard to the aft deck but rather through a small hole in
the side of the boat, say 1/2" for a 1/4" lanyard, so it could be
operated totally from inside the cabin.

Both Gerry's and Bob's boats used electric trolling motors. The plans
show rowing ports and no provisions for a motor. A boat like this
won't be a fast row boat but it might be useful in a calm. Even the
24' Birdwatcher would row about 2.5mph in a calm. But I'll admit that
adding a motor to Birdwatcher makes it a much more useful thing.

IMB takes two sheets of 1/2" plywood, eight sheets of 1/4" plywood
and one sheet of 3/16" Plexiglass. Taped seam construction using no
jigs or lofting.

Prototype News

Some of you may know that in addition to the one buck catalog which
now contains 20 "done" boats, I offer another catalog of 20 unbuilt
prototypes. The buck catalog has on its last page a list and brief
description of the boats currently in the Catalog of Prototypes.
That catalog also contains some articles that I wrote for Messing
About In Boats and Boatbuilder magazines. The Catalog of Prototypes
costs $3. The both together amount to 50 pages for $4, an offer you
may have seen in Woodenboat ads. Payment must be in US funds. The
banks here won't accept anything else. (I've got a little stash of
foreign currency that I can admire but not spend.) I'm way too
small for credit cards.

The out West Picara is I am told done to the point of using it as a
powerboat:

The down South Picara is more or less complete now. Should have an
updated photo soon.

This long and lean project is a 19' version of Toon2. Shown here on
its first sail in very light winds. We will wait a bit longer to
get a sailing report in stronger winds.

A Vector builder is keeping a website of the project at http://www.geocities.com/michsand@sbcglobal.net/
and here is a photo of his boat on its first sail, just before the
storm hit. I also have photos of a Vector completed by Pete
Mohylsky in Florida. Hopefully a report soon: